The present invention relates to methods and apparatus for performing quantitative analysis and, more particularly, to chromatography and the like.
Chromatographic instrumentation is extensively used for qualitative chemical analysis in the fields of medicine, pharmacology, toxicology, environmental monitoring, the petrochemical industry, and good production and quality control. The two types of instruments most widely used to perform these analyses are chromatographs and liquid chromatographs. Both utilize a specially prepared column to perform a physical separation of two or more compounds based upon their differential distribution between two phases; of which one is stationary and the other fluid. In addition to the column, a means must be provided to deposit the sample mixture on the column and to detect each component as it sequentially elutes from the column. The detector ideally provides an electrical output signal which is proportional to the quantity per unit time of the eluting sample components. The output signal over the period of the sample analysis is a series of peaks which are approximately Gaussian in shape, displayed on a potentiometric recorder or plotted from reconstructed digitized data. To relieve the investigator from the tedious and time consuming task of measuring the size of these peaks, many automatic measuring devices have been developed over the last 15 years. The first devices available were most commonly voltage-to-frequency converters coupled to counters with appropriate start/stop gating. As low cost microprocessors became available, these devices evolved into sophisticated digital signal processors.
The chromatographic data analysis systems that are presently on the market perform either or both a peak height or peak area measurement. These approaches are essentially automated versions of the traditional manually performed graphical methods. Consequently, these techniques can be generally applied to process any chromatographic peak, providing the signal-to-noise ratio is good. This requirement is necessary because peak height and area measurements are dependent on accurately defining the baseline upon which the peak is measured. Difficulty arises when the peak is small or asymetric or when the baseline is sloping or especially curved. Each of these problems must be individually handled by the data processor. Commercially available chromatographic analysis systems make extensive use of sometimes elaborate logic to extract meaningful data from what may be a poor quality chromatographic run. Equally important is the need to recognize the correct time within the sample run to apply the appropriate algorithm. The advent of microprocessor technology has considerably increased the performance-to-cost ratio for these more sophisticated versions. However, given the computation capability now available in relatively low cost microprocessor systems, a totally different approach becomes feasible for the measurement of chromatographic peaks.
A large number of applications involving the use of chromatographic instrumentation and the like require quantitative analysis on repetitive samples. Examples for the use of such analysis would be assays of a drug or drug metabolite in blood or urine, hospital clinical laboratory screening procedures, industrial process control and quality control, environmental pollution studies, and forensic applications. Each component can be recognized by its retention time. Quantitation can be based on the relative size of each peak to that of an internal standard, a related compound which is added to the sample initially in a precisely known amount. Data reduction can be optimized by estimation with maximum precision of the sizes of peaks appearing at pre-established times.
Wherefore, it is the object of the present invention to provide an improved method and apparatus for analysis by chromatography, or the like, which provides a best estimate of sample analysis by learning sample characteristics and applying them to later analysis.